Estimates of Spiral Ganglion Neuron Health in Children and Adults with Cochlear Implants

Abstract

Cochlear implants (CIs) can improve auditory perception for children and adults with severe to profound hearing loss, but little is known about how to optimize clinical interventions for individual patients. In fact, children and adults receive largely the same CI programming strategies despite their divergent hearing histories and auditory needs. Since CIs are designed to interface directly with the auditory nerve, knowledge of the physiological integrity of the spiral ganglion neurons (SGNs) may assist in developing patient-specific programming recommendations for children and adults. A series of experiments was conducted to quantify various aspects of SGN health in children and adults with CIs. Using the electrically evoked compound action potential (ECAP), the first two experiments determined whether local (within-ear) or global (across-ear) estimates of SGN density differ between child-implanted and adult-implanted listeners. A third experiment assessed the validity of using polarity sensitivity to infer the health of the peripheral processes in CI listeners, and a fourth experiment determined whether polarity sensitivity differed between children and adults with CIs. The results of these experiments suggested that young CI listeners who were deafened and implanted during childhood likely have denser populations of viable SGNs than older, adult-implanted listeners. However, deaf individuals may experience some degree of peripheral process degeneration regardless of their hearing history. The knowledge gained from these experiments suggests that optimal CI programming strategies may differ for children and adults. The results of this dissertation provide several avenues for future investigation of individualized programming parameters in listeners with diverse hearing histories.